Flexure based shock and vibration sensor for head suspensions in hard disk drives

ABSTRACT

Systems and methods for flexure based shock and vibration sensor for head suspensions in hard disk drives. Specifically, this invention deals with operational shock and vibration management within a hard disk drive. In one implementation, the assembly includes a circuit embedded optical waveguide sensor that includes a flexible electrical circuit board with a configuration of either a single or multi layers of conductor traces, a thin flexure gimbal for carrying and flying a HDD slider, a consecutive sensing layer constructed by an optical core and by clad construction with a configuration of either a single core array or a plural core array, an optical loop formed by light input and an output core, optical grating disposed on the consecutive sensing layer forming an optical grating waveguide sensor, a light emitter for injecting light into the optical core, and a receiver receiving the output light from the optical core.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 12/324,710, filed Nov. 26, 2008, which is based on and claims thebenefit of priority under 35 U.S.C. 119 from provisional U.S. patentapplication No. 61/016,769, filed on Dec. 26, 2007, the entiredisclosure of which is incorporated by reference herein.

FIELD OF THE INVENTION

This invention generally relates to data storage technology and morespecifically to operational shock and vibration management within a harddisk drive.

DESCRIPTION OF THE RELATED ART

With the increased use of data storage applications in portable consumerelectronic devices, such devices are required to deliver high mobilitywith stringent durability. The primary concerns for portable hard diskdrives (HDD), used in many portable consumer electronic devices, areshock performance and preventing loss of customer data.

Due to the inherent design features of HDDs, they are especiallysusceptible to external mechanical shocks. For example, HDD operationand slider head gimbal motion are highly dynamic and critical, due tothe slider head flying at a height of 5-18 nanometers above the magneticsurface of the disk. Shock induced slider head motion is the most commonfactor for data/media damage.

To prevent the head-media from crashing while track seeking, any largeshocks or vibrations occurring on the suspension gimbal need to bedetected in order to shut off the write gate and/or unload the slider toa ramp to prevent data/media damage. Most portable HDDs are equippedwith a shock sensor. However, due to the complexity of the HDDarchitecture, with the current state of the art, the sensor can only belocated on a rigid printed circuit board (PCB). Although such a sensorcan sense the HDD drop and shock, it is unable to sense motion occurringin the suspension or the head. Furthermore, false positive shockdetections can occur due to the remoteness of the sensor from the HDDhead. For example, a legitimate shock pulse could occur at the remotelocation, yet pose no risk to the head itself. This results in athroughput performance penalty.

SUMMARY OF THE INVENTION

The inventive methodology is directed to methods and systems thatsubstantially obviate one or more of the above and other problemsassociated with false sensing of shock and vibration due to the remoteposition of existing methods.

In accordance with one aspect of the present invention, there isprovided a hard disk drive (HDD) head carrying assembly including a baseplate mounted on a hard disk drive; and a trace gimbal assemblypivotally attached to the base plate and load beam. The aforesaid tracegimbal assembly includes a gimbal region rotably movable with respect tothe load beam; a thin flexure gimbal to carry and fly a HDD head, theHDD head disposed in a proximity of an edge of the gimbal assembly; aflexible electrical circuit board with a configuration in either singleor multi layers of conductor traces; and a strain sensor positionedbetween the point where the trace gimbal assembly is pivotally attachedto the base plate and the distal edge of the gimbal assembly.

In accordance with another aspect of the present invention, there isprovided a hard drive head carrying assembly including a base platemounted on a hard disk drive; and a trace gimbal assembly pivotallyattached to the base plate and load beam. The aforesaid trace gimbalassembly includes a gimbal region rotably movable with respect to theload beam; a flexure gimbal to carry and fly a HDD head; a flexibleelectrical circuit board; a free cantilevered portion, wherein the freecantilevered portion comprises a fixed end attached to at least aportion of the gimbal assembly and a free end; and at least one motionsensor mounted onto the free cantilevered portion.

Additional aspects related to the invention will be set forth in part inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. Aspects ofthe invention may be realized and attained by means of the elements andcombinations of various elements and aspects particularly pointed out inthe following detailed description and the appended claims.

It is to be understood that both the foregoing and the followingdescriptions are exemplary and explanatory only and are not intended tolimit the claimed invention or application thereof in any mannerwhatsoever.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification exemplify the embodiments of the presentinvention and, together with the description, serve to explain andillustrate principles of the inventive technique. Specifically:

FIG. 1 illustrates an exemplary diagram of a hard disk drive headcarrying assembly.

FIG. 2 illustrates an exemplary diagram of the various layers in thetrace gimbal of a head carrying assembly.

FIG. 3 illustrates an exemplary embodiment of a sensor placement inconjunction with a cantilever according to the present invention.

FIG. 4 illustrates an exemplary embodiment of a fixed-fixed beam sensorarrangement.

FIG. 5 illustrates critical geometry parameters that affect thewaveguide sensitivity.

FIG. 6 depicts a scheme for the flexure gimbal circuit embeddedwaveguide grating sensor.

FIG. 7 depicts an exemplary cross section view of a waveguide gratingsensor.

FIG. 8 illustrates an exemplary design scheme with a ring resonatorserving as a light return path.

FIG. 9 illustrates an exemplary design scheme utilizing an optical loopserving as a light return path.

FIG. 10 provides a simplified system scheme for the waveguide sensor.

FIG. 11 illustrates a multiple sensing arrangement in order to enableboth lateral and axial detection.

FIG. 12 illustrates an example of possible sensor locations.

DETAILED DESCRIPTION

In the following detailed description, reference will be made to theaccompanying drawing(s), in which identical functional elements aredesignated with like numerals. The aforementioned accompanying drawingsshow by way of illustration, and not by way of limitation, specificembodiments and implementations consistent with principles of thepresent invention. These implementations are described in sufficientdetail to enable those skilled in the art to practice the invention andit is to be understood that other implementations may be utilized andthat structural changes and/or substitutions of various elements may bemade without departing from the scope and spirit of present invention.The following detailed description is, therefore, not to be construed ina limited sense.

FIG. 1 illustrates a typical hard disk drive head carrying assembly, orhead gimbal assembly. A base plate/mount plate 100 is mounted onto thehard disk drive in order to carry the load beam or load arm 101. Theload beam holds the trace gimbal assembly 104, which holds the sliderhead 102 and flies it above the disk surface at a height of 5-18nanometers. Hinge regions 103 are dispersed onto the load beam to engageor disengage the slider.

FIG. 2 illustrates the various gimbal layers of the head carryingassembly. A trace gimbal flexure 204 is welded onto the load beam usingflexure welds. The trace gimbal flexure has an insulative polyimidelayer 205 on top of a SST layer 206. Electrically conductive traces 202reside on top of the polyimide 205, for transmission of signals to andfrom the head 207.

FIG. 3 illustrates an exemplary embodiment of a sensor placement inconjunction with a cantilever according to the present invention. In thepresent invention, an ideal location for co-locating the sensor fordetecting head motion is on the flexure gimbal circuit. Hence in FIG. 3,the sensor 300 is placed at the root of a cantilever beam 301 displacedin either the SST layer 306 or the polyimide layer 305 of the tracegimbal flexure. Electrically conductive traces 302 are provided fortransmission of signals to and from the head 207, and also forconnecting sensor 300 signals. Sensor 300 can be adhered to exposed padsin trace layer 302, with one trace being either grounded, or open,depending on the electronic sensing scheme. The cantilever ischaracterized with a fixed end and a free end. When shock or vibrationsare induced onto the head gimbal assembly and trace gimbal, the free endof the cantilever will displace, which is subsequently detected by thesensor located in the high strain region. This basic cantilevered membercan have many possible configurations, with the highest strain energycomponents being available at the root of the free beam. Various sensingmeans are also possible by strain detection (such as by strain gage orby a piezoelectric device), by other high gauge factor materials, or byoptical means.

Of course, other arrangements may be implemented and a cantilever ismerely one example. For example, FIG. 4 illustrates an exampleembodiment of a fixed-fixed beam sensor arrangement. The fixed-fixedbeam utilizes two fixed ends 402 with sensors 400 dispersed on or aboutthe beam. When the trace gimbal is functioning normally, the beamremains undeformed 401. However, when shock or vibrations are inducedinto the gimbal, the inertia of beam 401 will deform as depicted in 404,which is subsequently detected by the sensors. Other sensor locations405 are also possible within this configuration. Any number of sensorscould be introduced for shock sensing.

Another advantage of this invention is that the axis and orientation ofthe sensor rotates with the actuator arm. Radial shock is always purelyradial with the present invention. In contrast, a remotely locatedsensor, such as a sensor located on the main HDD PCB or the actuatorconnector, will have the head radial line of action rotating relative tothe sensing axis, depending on where on the disk the data is beingwritten or read. The outer diameter of the disk position can differ fromthe inner diameter position by as much as 40 rotational degrees.

Another advantage of this invention is that each head can have its ownsensor. So on a two platter, four head disk drive, there is tripleredundancy. Further, there is amplification inherent in sensing thevibrating cantilever or fixed-fixed beams. Typical damping in metalstructures is 0.5% of critical damping, which corresponds to a 100×amplification at the resonance frequency.

We describe the sensing mechanics, as being implemented into a centralregion of the flexure gimbal circuit and mid-span in the suspensionloadbeam, but any suitable location would fall within the scope andspirit of this invention. For example, other critical locations includelocations from the base plate all the way to an extension just beyondthe head itself.

An Example of the Optical Sensing Means

FIG. 5 illustrates critical geometry parameters that affect thewaveguide sensitivity. The characteristics of a light transmission in anoptical waveguide depend highly on the interface properties between thecore 500 and clad 501, in particular the reflective index delta.Creating an optical grating on the waveguide allows for the manipulationof light wavelength. Such gratings couple the fundamental mode with thecladding modes of the core, propagating in the same direction. Theexcited cladding-mode attenuates in the cladding core portion after thegrating, which results in the appearance of resonance loss in thetransmission spectrum. L=Grating Length, Λ=Grating Pitch, s=GratingWidth, di=Grating Depth, do=Clad thickness, and dc=core height.

Another major mechanism to induce light loss in the transmission isthrough photoelasticity manipulation. Based on the photoelastic effect,reflectivity is made to be proportional to strain, and light loss due tothe coupling of the cladding-mode is related to reflectivity. Whenmechanical loading is applied, Λ (period) is manipulated, i.e. theresonant wavelength changes with a change in period, Λ. Therefore,creating gratings on waveguide enables and further enhances themechanical loading (photoelastic) effect on the waveguide. This kind ofoptical structure could work as a sensor that responds to mechanical,thermal, as well as other environmental influences.

On example of a material and process that could fulfill the costproblems and yet meet key functional requirements, would be a Polymer(epoxy) Waveguide. By using a photosensitive polymer or epoxy and aphotolithography or laser direct imagining process to construct both theoptical waveguides and the electrical conductors on a hybrid circuit, itis possible to cost effectively mass fabricate a grating waveguidesensor on a gimbal trace, i.e., flexure gimbal circuit, for use in theHDD suspension. The present invention therefore provides a gimbal traceembedded shock sensor to be co-located on the HDD suspension.

In addition to the superiority on manufacturability and cost, opticalwaveguide sensors provide numerous engineering benefits on HDDapplication. Such benefits include immunity to electromagneticinterference (EMI), no data drifting, a linear response in a wide datarange, the potential to combine different kinds of sensors on awaveguide array, the capability of detecting temperature with adifferent grating design, having a miniature system with theemitter+sensor+receiver/+transceiver packed and sealed on a suspensionarm, easing of space limitations, and material cleanliness suitable fortypically stringent HDD requirements. With an integrated hybrid circuitprocess, the sensor is also directly embedded in circuit, therebygenerating a higher process yield than conventional types of sensorsthat require post assembly. The sensor is also flexible with a simplestructure to provide MEMS level sensitivity. Finally, fine resolutionsensing can be utilized, which makes the sensor capable of micro leveland real-time basis sensing.

Numerous benefits are achieved by using the present invention over MEMSand PZT shock sensors. For example, the present invention can beimplemented by using existing fabrication technologies, such asphotolithography and LASER direct imagining or e-beam writing. Theinvention can also be easily fabricated on an electrical flexiblecircuit board by being integrated into a semi-additive process ofCISFLEX™. In addition, the present invention can readily realize highprocess yield with micro level structure and cost saving by eliminatinga post sensor assembly. One or more of these benefits may be realizeddepending on the benefit. These and other benefits are describedthroughout the present specification and more particularly below.

The HDD suspension is a highly sophisticated and well optimizedmechanical slider carrier. Hence, any extra mass inertia or anyinappropriate geometry changes will cause resonant performancedegradation and penalty on lower G to lift-off. The current inventiontakes into account of critical parameters of a suspension and carefullyplans the configuration for a feasible sensor solution.

A corrugated geometry enhances the differential strain along thewaveguide core-clad interface which results in a larger wavecharacteristic change, thus enhancing the sensor sensitivity tomechanical loading. When subject to bending, the transmission gain dropsas bending increases with the intensity of the gain drop beingproportional to the resonant wavelength drop (due to the differentialstrain). The waveguide sensor presented here is capable of determiningmicro strain. The waveguide sensor also exhibits the samecharacteristics as bending when it is subjected to torsion, for examplein a cross-axis shock event. When tensile stress is applied, theresonant wavelength remains stable yet the transmission gain drop willbecome very sensitive to increases in tensile stress.

Such waveguide characteristics inspired the inventors to use aphotosensitive polymer or epoxy to form a waveguide grating sensor on asemi-additive electrical circuit board (in particular CISFLEX™), withthe integrated process which eliminates post sensor assembly on acircuit board that potentially results in higher yield and more accurateco-located sensing.

The scheme in FIG. 6 to FIG. 10 demonstrates the potential circuitembedded waveguide sensor configuration for HDD suspension motionsensing.

FIG. 6 depicts a scheme for the flexure gimbal circuit embeddedwaveguide grating sensor. In this figure, a configuration is shown todemonstrate a potential position on suspension loadbeam 600 to host thewaveguide sensor with the waveguide core 601 and clad 602, relative tothe polymide layer of the trace gimbal circuit 603 and stiffener or SSTlayer of the trace gimbal flexure 604. The design configuration here ismerely an example which should not unduly limit the applicability andscope of the claims herein. One of ordinary skill in the art wouldrecognize many other variations, modifications, and alternatives.

FIG. 7 depicts an example cross section view of a waveguide gratingsensor, depicting a potential design scheme incorporating the wave guidecore 701, the bottom clad 702, the top clad 704 and the stiffener or theSST layer of the trace gimbal flexure 703. This figure shows a potentialdesign scheme of a single-sided corrugated long-period grating waveguidesensor which contains materials and structures that are compliant with asemi-additive circuit process (in particular, CISFLEX™). Theconcentrated mass 700 which could be formed (for example by solderpaste) is optionally implemented to tune the sensor resonance as well asto enhance the sensor dynamic response by increasing inertia, therebybehaving as a tuned mass vibrator. Topology of the metal layer (such ascopper or stainless steel) could also be manipulated to tune the sensorresonance.

FIG. 8 illustrates an example design scheme with a ring resonatorserving as a light return path. A ring resonator 800 serves as a lightreturning path, utilizing an input core 801 and an output core 802, theyextend off of, or are mounted onto a portion of the polyimide and/or SSTtrace gimbal assembly. The symmetric pair of concentrated mass 803 couldenhance torsion response of the sensor as well as bending sensitivity.

Alternatively, FIG. 9 illustrates an example design scheme with anoptical loop serving as a light return path. The same principles in FIG.8 are adopted, but with a simple core u-turn 900 to form the lightreturn path. For the ease of illustration, the grating structure iseliminated from FIGS. 8 and 9. The design configurations demonstratedhere are merely examples which should not unduly limit the applicabilityand scope of the claims herein. One of ordinary skill in the art wouldrecognize many other variations, modifications, and alternatives.

FIG. 10 provides a simplified system scheme for the waveguide sensorthat can enable control signals to the disk drive electronics. Thesystem contains an emitter 1000 which can be a bright LED or a microsemiconductor laser chip or a vertical cavity surface emitting laser(VCSEL), and the receiver 1002 can be a photo diode and or a microspectrometer. Both emitter and receiver could be mounted on thesuspension arm or trace gimbal assembly with I/O provided by the hybridcircuit which potentially minimizes the entire optical sensor system andoptical losses, in case a lengthy waveguide is used. The light entersthe waveguide sensor 1001 from the emitter, and is received by thereceiver. The light received by the receiver is subsequently processedby the processing unit 1003. The system configuration depicted here ismerely an example, which should not unduly limit the scope of the claimsherein. One of ordinary skill in the art would recognize many othervariations, modifications, and alternatives.

FIG. 11 illustrates a multiple sensing arrangement in order to enableboth lateral and axial detection. As depicted in 1100, a dual sensorarrangement in series can be utilized to enhance the signal levelsensitivity if needed. Alternatively, multiple sensing can also beutilized as illustrated in 1101. In the illustration in 1101, threesensing elements 1102, 1103, and 1104, are utilized with 1102 and 1103in series with each other, 1102 and 1104 in series with each other and1103 and 1104 in parallel with each other. The result allows forenhanced sensitivity and lateral detection. For example, the sensingelement 1102 can behave as a reference element for 1103 and 1104,allowing the sensor to judge if the motion inflicted is lateral oraxial. Of course, such a configuration is merely an example and one ofordinary skill in the art would recognize many other variations,modifications, and alternatives.

FIG. 12 illustrates an example of possible sensor locations. Examples ofpossible sensor locations 1200 are indicated in the gridded areas of thefigure. However, the indicated locations are merely examples. The strainsensors as described may be positioned anywhere between the base plate1201 and the distal edge of the assembly (as indicated by sensorlocation 1202).

Moreover, other implementations of the invention will be apparent tothose skilled in the art from consideration of the specification andpractice of the invention disclosed herein. Various aspects and/orcomponents of the described embodiments may be used singly or in anycombination for sensing shock in the HDDs. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the invention being indicated by the followingclaims.

What is claimed is:
 1. A hard drive head (HDD) carrying assembly,comprising: a base plate mounted on a hard disk drive; and a tracegimbal assembly pivotally attached to the base plate and a load beam,the trace gimbal assembly comprising: a gimbal region rotably movablewith respect to the load beam; a flexure gimbal to carry and fly a HDDhead; a flexible electrical circuit board; a free cantilevered portion,wherein the free cantilevered portion comprises a fixed end attached toat least a portion of the gimbal assembly and a free end; and at leastone motion sensor which is an optical sensor mounted onto the freecantilevered portion.
 2. The hard drive head carrying assembly of claim1, further comprising a balance weight provided on the free cantileveredportion.